1. Field of the Invention
The present invention relates to a process cartridge and an image forming system on which such a process cartridge can be mounted. Such an image forming system may be embodied, for example, as an electrophotographic copying machine, a laser beam printer, a facsimile machine, a word processor or the like.
2. Related Background Art
In image forming systems such as copying machines, a latent image is formed by selectively exposing a uniformly charged image bearing member. The latent image is then visualized with toner and the toner image is transferred onto a recording sheet, thereby forming an image on the recording sheet. In such image forming systems, whenever the toner is used up, it must be replenished. The toner replenishing operation is not only troublesome, but also often causes contamination of the surroundings. Further, users are inconvenienced by the fact that the maintenance of various elements or members can be performed only by an expert in the art.
In order to eliminate such drawbacks and inconvenience, an image forming system wherein parts such as a developing device in which the toner therein has been used up or an image bearing member in which a service life thereof has expired, can easily be exchanged, thereby facilitating the maintenance, by assembling the image bearing member, a charger, the developing device and a cleaning device integrally as a process cartridge which can be removably mounted within the image forming system has been proposed and put into practical use, for example, as disclosed U.S. Pat. Nos. 3,985,436, 4,500,195, 4,540,268 and 4,627,701.
However, in the conventional art it was feared that there arose a discrepancy in distance between the original support plate and the surface of photosensitive drum, in accordance with the discrepancy in dimensional accuracy of each part and positional shift of the process cartridge in mounting thereof, thereby distorting the light image incident on the photosensitive member.
In the above-mentioned process cartridge, the following arrangement is known to enhance the positional accuracy between the image bearing member (photosensitive drum) and an optical means of the image forming system (as disclose in U.S. Pat. No. 4,972,227).
That is to say, it is known to arrange on a frame (of the process cartridge) for supporting the photosensitive drum, a positioning portion engageable by structure integral with the optical means attached to the image forming system when the process cartridge is mounted within the image forming system while shifting the process cartridge in an axial direction of the photosensitive drum. With this arrangement, it is possible to position the process cartridge with respect to the optical means of the image forming system with the least number of parts.